1. Field of the Invention
The present invention relates to an ink jet printer. The present invention further relates to a method for controlling the ink jet printer, and to a computer program product for executing that method.
The ink jet printer of the present invention includes an devices for printing words, images, etc. by discharging ink towards a print medium. For example, the ink jet printer of the present invention includes copying machines, fax machines, multifunctional products, etc.
2. Description of the Related Art
An ink jet printer has an ink jet head. Usually, the ink jet head has a nozzle, an ink chamber, a pressure chamber, and an actuator. The nozzle discharges ink toward a print medium. The ink chamber houses ink. The nozzle communicates with the ink chamber. The pressure chamber is disposed between the nozzle and the ink chamber. The actuator faces the pressure chamber. Usually, a piezoelectric element is used as the actuator.
Pulse signals that have at least two levels (high voltage and low voltage) are applied to the piezoelectric element. For example, a pulse signal having a high voltage, this being a base voltage, is applied. The piezoelectric element to which the pulse signal is applied changes voltage in the sequence: high voltage, low voltage, high voltage. When the piezoelectric element changes from high voltage to low voltage, the piezoelectric element deforms away from the pressure chamber. The volume of the pressure chamber thus increases, and pressure within the pressure chamber is decreased. Ink is drawn from the ink chamber into the pressure chamber. When the piezoelectric element changes from low voltage to high voltage, the piezoelectric element deforms towards the pressure chamber. The volume of the pressure chamber thus decreases, and pressure within the pressure chamber is increased. The pressurized ink is discharged from the nozzle. Usually, one ink droplet is discharged from the nozzle when one pulse signal is applied to the piezoelectric element.
An ink jet printer having the above configuration is taught in U.S. Pat. No. 6,808,254.
If ink dries out within an ink passage between the ink chamber and the nozzle, the ink may not be discharged correctly from the nozzle. The present invention uses a new technique to prevent the ink from drying out within an ink passage.